The Characteristics Of Autotrophic CO₂-fixing Microorganisms And Influence Factors In Soils And Groundwaters Of Huixian Karst Wetland

Huixian karst wetland is the largest natural karst wetland in China.In recent years,due to the influence of human activities,nitrogen pollution in groundwater and soil degradation have been aggravated.The study on autotrophic CO₂-fixing microorganisms in Huixian wetland is of great significance to the carbon sequestration,protection and restoration of karst wetlands.In this study,qPCR and high-throughput sequencing technologies were used to analyze the abundance of functional genes-cbbL and cbbM of Calvin cycle and the diversity of carbon-sequestered microbial community in karst groundwater at different nitrogen levels and in three states of native wetland.The study aims to explore the effects of nitrogen levels on the CO₂-fixing microbial community in karst groundwater,the characteristics of CO₂-fixing microbial communities in different states of Huixian karst wetland and the influence of soil organic carbon components on CO₂-fixing microbial communities.The main results are as follows:(1)A certain number of CO₂-fixing microorganisms containing cbbL and cbbM genes exist in the soil and groundwater of Huixian karst wetland.The abundance of cbbM gene in groundwater is higher than that of cbbL,while the abundance of cbbL gene in soil is higher than that of cbbM.The CO₂-fixing microorganisms is mainly made up of?-,?-,?-proteobacteria.In addition to use the Calvin cycle to complete their process of carbon sequestration,some dominant bacteria even participate in the nitrogen and sulfur cycle in the wetland system.(2)In the groundwater of Huixian wetland,the abundance of carbon-sequestered genes and community diversity are significantly affected by inorganic nitrogen.Nitrogen inflow may increase the number of CO₂-fixing microorganisms in groundwater but decrease the diversity;autotrophic denitrifying bacteria of Nitrosospira and Thiobacillus are concentrated in Huixian karst groundwater which is high in nitrogen and may participate in the removal of nitrogen pollution in the water body;in addition,the structure of CO₂-fixing microorganisms in groundwater is also significantly affected by environmental factors such as DOC,DIC and temperature.(3)In the soil of Huixian karst wetland,the composition of CO₂-fixing microorganisms in the three states of native wetland,naturally degraded wetland and post-cultivated wetland is basically similar,but the relative abundance of some dominant bacteria is significantly different.The physicochemical properties of the soil in different states of Huixian vary from each other,and this variety significantly changed the structure of soil CO₂-fixing microorganisms.The soil organic carbon components(SOC,DOC,MBC,ROC)and T were the main influencing factors.In summary,the changes in wetland environmental factors caused by human activities(such as wetland reclamation,application of nitrogen fertilizer,etc.)have significantly influenced the abundance of functional genes-cbbL and cbbM and the structure and diversity of CO₂-fixing microorganisms in the soil and groundwater in the Huixian karst wetland system.The results of this thesis have a certain scientific significance for understanding the role of microorganisms in the element cycle of karst wetlands,and provide a scientific basis for wetland protection.